Simplified upper electrode contact structure for PIN diode active pixel sensor

ABSTRACT

An active pixel sensor having a transparent conductor that directly contacts a conductive element in an interconnection structure to electrically connect the transparent conductor to a pixel sensor bias voltage is provided. The active pixel sensor includes a semiconductor substrate, the interconnection layer, which is formed over the substrate, and a pixel interconnection layer formed over the interconnection layer. Photo sensors that include a pixel electrode, an I-layer, and may include a P-layer are formed over the pixel interconnection layer. The transparent conductor is formed over the photo sensors and the conductive element exposed on the surface of the interconnection layer.

This is a divisional of application Ser. No. 09/810,852, filed Mar. 16,2001 now U.S. Pat. No. 6,649,993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to PIN photo diode active pixelsensors. In particular, the present invention relates to an elevated PINdiode sensor with a simplified upper electrode contact structure.

2. Description of the Background

Image sensors such as charged coupled devices (CCDs) and active pixelsensors are used in a wide range of applications such as digitalcameras, camcorders, and night vision enhancement systems. In theseapplications, light detected at an array of such image sensors isconverted to electrical signals that have amplitudes proportional to theintensity of the light. Thus, the image sensors can convert an opticalimage into a set of electronic signals. The electronic signals mayrepresent intensities of colors of light received by the image sensors.The electronic signals can be conditioned and sampled to allow imageprocessing.

Integration of the image sensors with signal processing circuitry isbecoming more important because integration enables miniaturization andsimplification of imaging systems. Integration of image sensors alongwith analog and digital signal processing circuitry allows electronicimaging systems to be low cost, compact, and require low powerconsumption.

Historically, image sensors have predominantly been CCDs. CCDs arerelatively small and can provide a high-fill factor. However, CCDs arevery difficult to integrate with digital and analog circuitry.Furthermore, CCD systems dissipate large amounts of power and sufferfrom image smearing problems.

Active pixel sensors are an alternative to CCD sensors. Active pixelsensors can be fabricated using standard CMOS processes. Therefore,active pixel sensors can easily be integrated with digital and analogsignal processing circuitry. Further, CMOS circuits dissipate smallamounts of power.

FIG. 1 shows a cross-section of a prior art array of image sensors. Thisarray of image sensors includes PIN diode sensors located over asubstrate 10. An interconnection structure 12 electrically connects anN-layer (N-type layer) 14 of the PIN diodes to the substrate 10, such asa silicon substrate. An I-layer (intrinsic layer) 16 is formed over theN-layer 14. A P-layer (P-type layer) 18 is formed over the I-layer 16.The P-layer 18, the I-layer 16 and the N-layer 14 form the array of PINdiode sensors. A first conductive via 20 electrically connects a firstdiode sensor to the substrate 10, and a second conductive via 22electrically connects a second diode sensor to the substrate 10. Atransparent conductive layer 24 is located over the array of diodesensors. A conductive lead 26 is connected to the transparent conductivelayer 24. The conductive lead 26 is connected to a bias voltage thatallows biasing of the P-layer 18 of the array of PIN diode sensors to aselected voltage potential.

A limitation of the image sensor structure of FIG. 1 is the electricalconnection between the conductive lead 26 and the transparent conductivelayer 24. The transparent conductive layer 24 must be electricallyconductive to allow biasing of the PIN diodes, and must be transparentto allow the PIN diodes to receive light. Generally, it is verydifficult to bond to the types of materials that must be used to formthe transparent conductive layer 24. Therefore, the conductive lead 26must be attached to the transparent conductive layer 24 with the aid ofsome type of clamp or support structure. The result is an electricalconnection which is not reliable and which is expensive to produce.

It is desirable to have an active pixel sensor formed adjacent to asubstrate in which a transparent conductor is reliably electricallyconnected to a pixel sensor bias voltage which originates on thesubstrate.

SUMMARY

An active pixel sensor is provided that includes a semiconductorsubstrate, an interconnection structure adjacent to the substrate, and asensor interconnect structure adjacent to the interconnection structure.Photo sensors that contain individual pixel electrodes and an I-layerare formed over the sensor interconnect structure. A transparentconductor is deposited over both the photo sensors and an exposedconductive element in the interconnection structure. The conductiveelement passes through the interconnection structure to the substrateand allows a pixel sensor bias voltage that originates from circuitrywithin the substrate to be applied to the transparent conductor. Asecond conductive element in the interconnection layer is left exposedto allow connection to external packaging or other devices.

The substrate may contain active circuits to sense charge accumulationby the photo sensors due to the photo sensors receiving light. The photosensors may include an additional P-layer formed between the I-layer andthe transparent conductor, with the inner surface of the transparentconductor electrically connected to the P-layer, the I-layer, and thepixel interconnect layer.

In one embodiment, the semiconductor substrate contains a junctioncontact layer over which the interconnection structure has been removed.The transparent conductor is deposited over the photo sensors and theexposed junction contact layer in the substrate itself. This allows apixel sensor bias voltage that originates from circuitry within thesubstrate to be applied directly to the transparent conductor.

In one embodiment, the active pixel sensor is formed by forming theinterconnection structure adjacent the substrate and the sensorinterconnect structure adjacent the interconnection structure. At leastone pixel electrode is formed adjacent the sensor interconnect structureand an I-layer is deposited over the at least one pixel electrode andpixel interconnect layer. A portion of the I-layer and pixelinterconnect layer is removed to expose the conductive element. Atransparent conductor is deposited over the I-layer and conductiveelement.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a cross-section of a prior art array of imagesensors.

FIG. 2 is a cross-sectional view of an active pixel sensor in accordancewith an embodiment of the invention.

FIG. 3 is a cross-sectional view of an active pixel sensor in accordancewith another embodiment of the invention.

FIG. 4 is a cross-sectional view of a substrate with an interconnectionstructure and sensor interconnect structure formed over the substrate.

FIG. 5 is a cross-sectional view of pixel electrodes deposited on thesensor interconnect structure illustrated in FIG. 4.

FIG. 6 is a cross-sectional view of an I-layer and P-layer depositedover the pixel electrodes illustrated in FIG. 5.

FIG. 7 is a cross-sectional view showing the I-layer, P-layer and pixelinterconnect layer of FIG. 6 selectively etched to expose a conductivecontact region in the interconnection structure.

FIG. 8 is a cross-sectional view of a transparent conductor depositedover the structure illustrated in FIG. 7.

FIG. 9 is a cross-sectional view showing the I-layer, P-layer and pixelinterconnect layer of FIG. 6 selectively etched to expose both theconductive contact region and bond pad in the interconnection structure.

FIG. 10 is a cross-sectional view of a transparent conductor that hasbeen deposited over the structure illustrated in FIG. 9 and selectivelyetched from bond pad 65.

FIG. 11 is a cross-sectional view showing the I-layer, P-layer, andpixel interconnect layer of FIG. 6 selectively etched to expose both aconductive contact region and bond pad in the interconnection structure.

FIG. 12 is a cross-sectional view of a transparent conductor depositedover the structure illustrated in FIG. 11 and selectively etched fromone of the bond pads.

DETAILED DESCRIPTION

FIG. 2 shows one embodiment of an active pixel sensor 200. In sensor200, the transparent conductor 50 directly contacts conductive element56, 57 in an interconnection structure 42 to electrically connect thetransparent conductor 50 to a pixel sensor bias voltage that originatesin the substrate 40.

In the structure of sensor 200, the interconnection structure 42 isformed adjacent to the substrate 40. A sensor interconnect structure 43is formed adjacent to the interconnection structure 42. Each pixelsensor of an array of pixel sensors includes an individual pixelelectrode 44 and an inner metal section 45. Pixel electrodes 44 and theinner metal section 45 are formed adjacent to the sensor interconnectstructure 43. Each individual pixel electrode 44 is electricallyconnected to the substrate 40 through individual conductive vias 52, 54in the sensor interconnect structure 43. An I-layer (intrinsic layer) 46is formed adjacent to the pixel electrodes 44. A P-layer (P-type layer)48 is formed adjacent to the I-layer 46.

A transparent conductor 50, which may be any conductive contact layer,is formed adjacent to the P-layer 48. The transparent conductor 50 iselectrically connected to the substrate 40 through direct contact with aconductive element 56, 57 in the interconnection structure 42. In thesensor 200 illustrated in FIG. 2, the conductive element is shown as aconductive contact region 56, e.g., a bond pad, and metal plug 57.However any conductive element, such as a metal line, that passesthrough the interconnection structure 42 may be used to form theelectrical connection to the substrate 40.

Sensor structure 200 generally includes additional conductive elements,such as bond pad 65, that do not contact conductor 50 and allowconnection of the sensor to packaging or other external device.

The pixel sensors are photo sensors that conduct charge upon receivinglight. The substrate 40 generally includes sense circuitry and signalprocessing circuitry. The sense circuitry senses how much charge thepixel sensors have collected during a “shutter” period. The amount ofcharge conducted represents the intensity of light received by the pixelsensors during the shutter period. Generally, the substrate circuitrycan be CMOS (complementary metal oxide silicon), BiCMOS or Bipolar andcan be any compound semiconductor such as, e.g., GaAs or InP. Thesubstrate can include various types of substrate technology includingcharged coupled devices.

Typically, the interconnection structure 42 is a standard CMOSinterconnection structure. The structure and methods of forming thisinterconnection structure are well known in the field of electronicintegrated circuit fabrication. The interconnection structure 42 can bea subtractive metal structure, or a single or dual damascene structure.

The sensor interconnect structure 43 is typically formed from siliconoxide or a silicon nitride with metal filled vias. The sensorinterconnect structure 43 provides reliability and structural advantagesto the pixel sensor structure. The pixel interconnect structure allowsfor the formation of thin pixel electrodes 44 because the pixelelectrodes 44 are formed over silicon rather than a metal pad located onthe interconnection structure 42. The pixel interconnect structure 43electrically connects the pixel electrodes 44 to the interconnectionstructure 42.

The conductive vias 52, 54 pass through the sensor interconnectstructure 43 and electrically connect the pixel electrodes 44 to thesubstrate 40. The sensor interconnect structure 43 allows thisinterconnection circuitry to be tightly packed because the vias 52, 54are located directly underneath the pixel electrodes, which conserveslateral space. Additionally, the sensor interconnect structure 43 allowsthe formation of vias 52, 54 having a minimal diameter. Typically,conductive vias 52, 54 having a minimal diameter are formed fromtungsten using a CVD process. Tungsten is generally used duringfabrication because tungsten can fill high aspect ratio holes. That is,tungsten can be used to form narrow and relatively longinterconnections. However, the temperatures required to form tungstenvias with a CVD process are greater than many of the materials(amorphous silicon for example) used to form the pixel electrodes canwithstand. By forming the sensor interconnect structure 43 over thesubstrate 40, and the pixel electrodes 44 over the sensor interconnectstructure 43, the vias 52, 54 can be formed before the pixel electrodes44, and thus, the pixel electrodes 44 are not subjected to the hightemperatures required for the formation of vias 52, 54. Other materialsthat may be used to form the conductive vias 52, 54 include copper,aluminum, or any other electrically conductive material.

The inner metal section 45 typically includes a thin conductivematerial. The inner metal section 45 may be formed, for example, from adegenerately doped semiconductor layer, aluminum, titanium, titaniumnitride, copper or tungsten. The inner metal section 45 should be thin(approximately 500 angstroms) and smooth. The inner metal section 45should be smooth enough so that any surface roughness is substantiallyless than the thickness of the pixel electrode 44 formed over the innermetal section 45. To satisfy the smoothness requirement, polishing ofthe inner metal section 45 may be required.

The inner metal section 45 can be optional. However, the inner metalsection 45 has a lower resistance than the materials used to form thepixel electrodes 44. Therefore, the inner metal section 45 providesbetter current collection.

The pixel electrodes 44 are generally formed from a doped semiconductor.The doped semiconductor can be, for example, an N-layer (N-type layer)of amorphous silicon, which may be doped with, for example, phosphorous.Alternatively, the pixel electrodes 44 can be implemented with aconductive nitride, e.g., titanium nitride. The pixel electrode must bethick enough and doped heavily enough so that the pixel electrodes 44 donot fully deplete when biased during operation.

Although an N-layer of amorphous silicon is typically used when theactive pixel sensors have a PIN diode configuration, the active pixelsensors can include an NIP sensor configuration. In this case, the pixelelectrodes 44 are formed from a P-layer, and the P-layer 48 of FIG. 2 isreplaced with an N-layer.

The sensor 200 includes an I-layer 46 that is typically formed from ahydrogenated amorphous silicon. I-layer 46 is electrically connected tothe transparent conductor 50. The I-layer includes a resistive pathbetween the electrodes 44 and the transparent conductor 50. Theresistance of the resistive path between the end electrode (theelectrode 44 electrically connected to the conductive via 54) and thetransparent conductor 50 is directly dependent on the distance 47.Increasing the resistance minimizes leakage current-that flows throughthe resistive path. Therefore, the end electrode should be located sothat a distance 47 between the edge of the end electrode and thetransparent conductor 50 is maximized.

The P-layer 48 is generally formed from amorphous silicon. Typically,the P-layer 48 is doped with Boron. The P-layer 48 thickness mustgenerally be controlled to ensure that the P-layer 48 does not absorbtoo much short wavelength (blue) light.

Another embodiment of sensor 200 does not include a P-layer 48. TheP-layer can be eliminated with proper selection of the composition ofthe material within the transparent conductor 50, and proper selectionof the doping levels of the pixel electrodes 44. For this embodiment,the transparent conductor 50 provides a conductive connection between atop surface of the I-layer 46 of the pixel sensors and theinterconnection structure 42, rather than just between an edge surfaceof the I-layer 46 and the interconnection structure 42.

As previously described, the pixel electrodes 44, the I-layer 46, andthe P-layer 48 are generally formed from amorphous silicon. However, thepixel electrodes 44, the I-layer 46, and the P-layer 48 can also beformed from amorphous carbon, amorphous silicon carbide, amorphousgermanium, or amorphous silicon-germanium. It should be understood thatthis list is not exhaustive.

The transparent conductor 50 provides a conductive connection betweenthe P-layer 48 and the I-layer 46 of the pixel sensors, and theinterconnection structure 42. Transparent conductor 50 is typicallytransparent to light in the visible wavelength range, but, as sensor 200may be constructed to detect various wavelengths of electromagneticradiation, e.g., x-rays, transparent conductor 50 need only betransparent to the relevant wavelengths, and may be any conductivecontact layer.

Light that is received by the pixel sensors must pass through thetransparent conductor 50. Both the selection of the type of material tobe used within the transparent conductor 50, and the determination ofthe desired thickness of the transparent conductor 50, are based uponminimizing the reflection of light received by the pixel sensor.Minimization of the reflection of light received by the pixel sensorhelps to optimize the amount of light detected by the pixel sensor.Transparent conductor 50 is typically formed from an indium tin oxide,but may also be formed from titanium nitride, thin silicide, or certaintypes of transition metal nitrides or oxides.

A protective layer may be formed over the transparent conductor 50. Theprotective layer provides mechanical protection, electrical insulation,and can provide some anti-reflective characteristics, and is typicallyformed from a thin dielectric film such as SiO₂, which may be, forexample, 5,000 angstroms thick.

Another embodiment includes Schottky diode sensors. Schottky diodesensors include several different configurations. A first Schottky diodeconfiguration includes the electrodes 44 being formed from a conductivemetal. This configuration also includes the I-layer 46 and the P-layer48. A second Schottky diode configuration includes the electrodes 44being formed from a conductive metal and the P-layer 48 being replacedwith a transparent conductor or a transparent silicide. A third Schottkydiode configuration includes the electrodes 44 being formed from anN-layer, and the P-layer being replaced with a transparent conductor.The transparent conductor of the third configuration must exhibit aproper work function. Conductive metals that may be used for theSchottky configurations include, but are not limited to, chrome,platinum, aluminum and titanium.

FIG. 3 illustrates another embodiment for an active pixel sensor. Sensor300 is similar to sensor 200 except that instead of using conductiveelement 56, 57 through interconnection structure 42 to electricallyconnect transparent conductor 50 to substrate 40, transparent conductor50 directly contacts the substrate 40. The semiconductor substrate 40has, for example, a junction contact layer 58 made from, e.g., titaniumsilicide, that is electrically connected to a pixel sensor voltage thatoriginates in circuitry within the substrate 40. The physical contactbetween the transparent conductor 50 and the junction contact layer 58electrically connects the transparent conductor 50 to the pixel sensorvoltage.

FIGS. 4-8 illustrate a process sequence that can be used to fabricate anactive pixel sensor 200 as illustrated in FIG. 2.

FIG. 4 shows a substrate 40 with a standard interconnection structure 42and a sensor interconnect structure 43 formed over the substrate 40. Themethods of forming structures 42, 43 are well known in the field ofelectronic integrated circuit fabrication. The interconnection structure42 can be a subtractive metal structure, or a single or dual damascenestructure, and typically includes metal plugs 57, conductive contactregions 56, or other conductive element such as metal lines, and bondpads 65. The conductive vias 52, 54 are typically formed using achemical vapor deposition (CVD) process of tungsten or other metal.

FIG. 5 shows pixel electrodes 44 and inner metal sections 45 depositedon the sensor interconnect structure 43. An inner metal layer and apixel electrode layer are first deposited on the sensor interconnectstructure 43. The pixel electrode layer and an inner metal layer arethen etched according to a predetermined pattern to form the pixelelectrodes 44 and the inner metal layers 45. An individual pixelelectrode 44 and inner metal section 45 are formed for each pixelsensor.

The pixel electrodes 44 are typically deposited using plasma enhancedchemical vapor deposition (PECVD). The PECVD is performed with aphosphorous containing gas, for example, PH₃. A silicon containing gas,such as Si₂H₆ or SiH₄, is included when forming amorphous silicon pixelelectrodes 44. The predetermined pixel electrode pattern is formedthrough a wet or dry etch of the deposited pixel electrode material.

FIG. 6 shows an I-layer 46 and a P-layer 48 deposited over the pluralityof pixel electrodes 44. The I-layer 46 is generally deposited using aPECVD or reactive sputtering process. The PECVD must include a siliconcontaining gas. The deposition should be at a low enough temperature sothat hydrogen is retained within the film. The P-layer 48 can also bedeposited using PECVD. The PECVD is performed with a Boron containinggas, for example B₂H₆. A silicon containing gas is included when formingan amorphous silicon P-layer 48.

FIG. 7 shows the P-layer 48 and the I-layer 46 having been etched toremove these layers from the portion of the interconnect structure 43which lies over the conductive contact region 56 and bond pad 65. Thesensor interconnect structure 43 is then selectively etched from theregion over conductive contact region 56 to expose conductive contactregions 56. As discussed above, the conductive contact region 56 iselectrically connected to a reference voltage on the substrate 40 thatis used to bias the array of pixel sensors.

FIG. 8 shows the transparent conductor 50 deposited over the P-layer 48and conductive contact region 56 to provide an electrical connectionbetween the P-layer 48, the I-layer 46, and the substrate 40. Thetransparent conductor 50 is generally deposited through a reactivesputtering process, which is well known in the art of integrated circuitfabrication. However, the transparent conductor 50 can also be grown byevaporation. If the transparent conductor 50 is formed from titaniumnitride, then typically a CVD process or a sputtering process must beused to deposit the transparent conductor 50.

The transparent conductor 50 and the sensor interconnect structure 43are then etched according to a predetermined pattern to exposeadditional conductive elements such as bond pad 65. This etching allowsaccess to the additional conductive elements of the interconnectionstructure 42, resulting in the structure of sensor 200 illustrated inFIG. 2.

To form the sensor structure 300 illustrated in FIG. 3, a similarprocess sequence as that illustrated in FIGS. 4-8 may be used with somemodification. The formation of conductive element 56, 57 ininterconnection structure 42 is unnecessary. Additionally, when etchingthrough the sensor interconnect structure 43, as illustrated in FIG. 7,the etch is continued to remove a portion of the interconnectionstructure 42 over the junction contact layer 58 (shown in FIG. 3), toexpose the junction contact layer on the surface of substrate 40.Transparent conductor 50 is then deposited and etched as described abovein reference to FIG. 8.

FIGS. 9 and 10 illustrate another process sequence that may be used toform the active pixel sensors. In this embodiment, after depositing theI-layer 46 and P-layer 48, as was illustrated in FIG. 5, portions of theI-layer 46 and P-layer 48 which are not part of the photo sensor diode(e.g., not over pixel electrodes 44) are selectively etched from thestructure. The interconnection structure 42 is then selectively etchedto remove interconnection structure 42 that is over the conductivecontact region 56 and bond pad 65, as illustrated in FIG. 9.

A layer of transparent conductor 50 is then deposited over the entirestructure of FIG. 9, and then patterned to remove conductor 50 fromeverywhere except over the photo sensor diode and conductive contactregion 56, leaving sensor structure 400 as illustrated in FIG. 10. Thus,in sensor 400, the transparent conductor 50 remains only over the photosensor and conductive element 50, which may reduce the likelihood ofshorting the active pixel sensor when making contact to bond pad 65.

In the process sequence illustrated in FIGS. 4-8 and 9-10, two selectiveetches are needed to obtain the structures illustrated in FIG. 7 andFIG. 9. A portion of the I-layer 46 and P-layer 48 is first selectivelyetched from the region that is over the conductive contact region 56 andbond pad 65. A portion of the sensor interconnect structure 43 is thenselectively etched from the region over conductive contact region 56, asshown in FIG. 7, or from both the region over conductive contact region56 and bond pad 65, as shown in FIG. 9. This process sequence may besimplified, as illustrated in FIGS. 11 and 12.

After depositing the I-layer 46 and P-layer 48, as was illustrated inFIG. 6, the portion of the I-layer 46, P-layer 48, and sensorinterconnect structure 43 that is over both conductive contact region 56and bond pad 65 can be entirely removed, as illustrated in FIG. 11.These layers may be removed in a single etch, which is typically a wetor dry chemical etch as described above.

The transparent conductor 50 is then deposited over the P-layer 48 andthe exposed conductive contact region 56 and bond pad 65. Thetransparent conductor 50 is subsequently etched according to apredetermined pattern to expose to bond pad 65 of the interconnectionstructure 42, resulting in active pixel sensor structure 500 of FIG. 12.The sensor structure 500 can thus be formed with fewer processing stepsthan the sensor structure 200 of FIG. 2. However, sensor interconnectstructure 43 may contain a passivation layer, so removal of the entirelayer as illustrated in FIG. 11 may leave the sensor 500 unpassivated.

As stated previously, after deposition of transparent conductor 50, aprotective layer (not shown) may be formed over the transparentconductor 50 using conventional methods. The protective layer providesmechanical protection and electrical insulation, and can provide someanti-reflective characteristics.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects. Therefore, the appended claims are toencompass within their scope all such changes and modifications as fallwithin the scope of this invention.

1. A method of forming an active pixel sensor comprising the acts of:providing a semiconductor substrate; forming an interconnectionstructure adjacent the semiconductor substrate said having a firstconductive element that passes through the interconnection structure tothe substrate; forming a sensor interconnect structure adjacent theinterconnection structure; forming at least one pixel electrode adjacentthe sensor interconnect structure; depositing an intrinsic layer overthe at least one pixel electrode; removing a portion of the intrinsiclayer and a portion of the sensor interconnect structure to expose thefirst conductive element; and after said removing, depositing aconductive contact layer over the intrinsic layer and the exposed firstconductive element, wherein an inner surface of the conductive contactlayer is physically and electrically connected to the intrinsic layer,and the inner surface of the conductive contact layer is physicallyconnected to the first conductive element to electrically connect theconductive contact layer to the substrate.
 2. The method of forming anactive pixel sensor of claim 1, wherein the first conductive elementcomprises a bond pad and a metal plug.
 3. The method of forming anactive pixel sensor of claim 1, wherein the at least one pixel electrodeand the intrinsic layer form a photo sensor and the substrate comprisesactive circuits that sense charge accumulated by the photo sensor due tothe photo sensor receiving light.
 4. The method of forming and activepixel sensor of claim 1, wherein forming the at least one pixelelectrode comprises: depositing an inner metal layer over the sensorinterconnect structure; depositing a pixel electrode layer over theinner metal layer; and etching the pixel electrode layer and inner metallayer according to a predetermined pattern.
 5. The method of forming anactive pixel sensor of claim 4, wherein the pixel electrode layer is anN-type layer.
 6. The method of forming an active pixel sensor of claim4, wherein the pixel electrode layer is a P-type layer.
 7. The method offorming an active pixel sensor of claim 1, wherein the interconnectionstructure comprises a second conductive element, the method furthercomprising removing a portion of the intrinsic layer, a portion of thesensor interconnect structure and a portion of the conductive contactlayer to expose the second conductive element.
 8. The method of formingan active pixel sensor of claim 1, further comprising depositing aP-type layer onto the intrinsic layer, the inner surface of theconductive contact layer electrically connected to the P-type layer, theintrinsic layer, and the sensor interconnect structure, the methodfurther comprising etching the P-type layer to expose the firstconductive element.
 9. The method of forming an active pixel sensor ofclaim 8, wherein the P-type layer comprises amorphous silicon.